THE 



OB 

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NlV92L OUNG ASTRONOMER. 




BY SAMUEL WORCESTER. 



ILLUSTRATED WITH CUTS. 



Boston: 

RICHARDSON, LORD AND HOLBROOK. 

1831. 



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St Si 




YO 



UNG ASTRONOMER, 



DESIGNED FOR 



>V- 



COMMON SCHOOLS, 



ILLUSTRATED BY CUTS. 




_^_ 



BY SAMUEL WORCESTER. 

AUTHOR OF SEVERAL POPULAR SCHOOL BOOKS. 






BOSTON: 

RICHARDSON, LORD AND HOLBROOK, 

133 Washington Street. 

1831. 






* ■ - • 4 ■ <* 'It \ 



• ♦ ** * ^Ul '^fa*"**''** s % - 



Entered according to act of Congress, in the year 1831, by Richardson. 
Lord & Holbrook, in the Clerk's Office of the District of Massachusetts. 



Ssf 



/£- 



iCP The following books are particularly recommended to the 

notice of Teachers and others. 

Worcester's Primer. 

Second Book for Reading and Spelling. 

Pierpont's Young Reader. 

Introduction to the National Reader. 

National Reader. 

The Juvenile Lyre, or Hymns and Songs, set to appropriate 
Music for Common Schools, by L. Mason. 

The First Book of History, or History on the basis of Geogra- 
phy. Being the History of all the Countries in North and 
South America, illustrated and rendered attractive and in- 
teresting to children by the introduction of Anecdotes, 
sixty Cuts, and sixteen beautiful Maps from steel plates. By 
the Author of Peter Parley's Tales. 



a 1 
: 



REMARKS TO TEACHERS. 



We do not give to children the abstract, philosophical principles of 
the several sciences. They are first taught the most interesting and 
useful facts belonging to each science ; and, as their minds become 
more perfectly formed, we introduce the more abstruse phenomena and 
principles. The science of Astronomy seems not, however, to have 
been so far divested of its more difficult parts, as to be adapted to our 
' Common Schools ; and, therefore, our children grow up in ignorance 
of much valuable truth relating to this subject, which they are capable 
of receiving. 

It may be of use to Teachers, to remark that the author designed 
this little work for those children, who have once properly studied 
their larger Geography. It is believed that all such children will be 
found capable of understanding so much of Astronomy as is treated 
of in this book ; and it will assist them in understanding many parts of 
Geography. After studying this work, they may review the two sci- 
ences separately, or in connexion with each other, as may be found 
most convenient. 

Although this work is particularly designed for schools, and is there- 
fore a book for study rather than simple reading, yet, those who have 



,<. 



IV REMARKS TO TEACHERS. 

not leisure to study it regularly, may derive from it much information. 

« 
And it is recommended that even persons of this class should pay par- 
ticular attention to the questions at the end of each paragraph. They 
will thereby be greatly assisted in understanding what are the leading, 
practical truths, which the author designed to teach. 

The mode of questioning here presented is thought to be well adapt- 
ed, to make the scholar learn his lessons thoroughly, and to be well 
suited to this science. The teacher will find it useful, to add many 
other questions and examples ; but each part of a lesson should receive 
its proper share of attention, and caution should be used, that leading 
facts and principles be not lost in a display of minor facts and circum- 
stances. 

The last two chapters are shorter than was designed, because less 
room was left for them than was expected. But they are not among 
the most important parts of the work ; and the obliging Teacher will 
not find it difficult to supply the few facts which are here omitted. 



ASTRONOMY. 



INTRODUCTORY CHAPTER. 

1. Astronomy treats of the Sun, Moon, Planets, Stars, 
and other heavenly bodies. Before you can well understand 
what we have to say about these wonderful things, you must 
learn the meaning of a few words that we shall often use. 
You must also have a ball, with a hole through its middle, 
and a stick in it. An apple or an orange will answer the 
purpose ; but a wooden ball will be better. 

What does Astronomy treat of? 

2. Your ball is a globe or sphere. Everything, whether 
great or small, that is shaped like a ball, is called a globe or 
sphere. An apple, an orange, this great Earth on which we 
live, the Moon, the Planets, and the Sun are all shaped in 
nearly the same manner, and we therefore say that they are 
globular or spherical. 

What is a globe ? Mention several spheres, both large and small. 

3. We cannot make a good picture of a ball on paper, but 

A 



ASTRONOMY. 



this will help to explain some things respecting your wooden 
ball; and all other globes. 

4. The axis of a 
globe is a line passing 
through its centre, as 
the hole or stick goes 
through your ball ; and 
when the globe turns 
round, it turns on its 
axis. 

5. Mark N. and S. 
on the ball as they are 
marked in the picture, 
and hold it so that N. 
will point to the North, 
and S. to the South ; and call those parts of the ball the 
North Pole and the South Pole. 

What is the end of the axis called, which points to the north ? 
What is the opposite end called ? 

6. The equator is a line surrounding a globe at an equal 
distance from each pole. Make a mark with a piece of chalk, 
or pass a string round your ball in this manner, and it will 
represent its equator. The term equator commonly denotes 
a line round the globe on which we live, at an equal distance 
from the North Pole and the South Pole. 

What is the equator % 




DEFINITIONS. 7 

7. The diameter of a globe is any straight line passing 
through the middle of it, as the stick runs through the ball. 
So also any straight line passing through the centre of a 
circle, from one side to the other, is its diameter. 

What is the diameter of a globe or a circle ? 

8. The circumference of a globe is the distance around it 
in the middle. Thus the equator measures the circumference ; 
and a line passing round the middle in any other direction, 
will do the same. 

What is the circumference of a globe ? 

9. The circumference of a globe or a circle, is about three 
times as great as its diameter. 

If your ball is two inches in diameter, what is its circumference ? If 
the diameter were 1 foot, what would be the circumference ? The 
Earth is about 8 thousand miles in diameter ; what is the distance 
round it ? If a hoop is 9 feet in circumference, what is its diameter? 
I once measured round a tree, and found the distance 24 feet 9 inches; 
what was its diameter ? 

10. You can see that the circumference of any globe is a 
circle. Thus, the equator is a circle, and any line drawn in a 
similar manner round your ball, is a circle. We divide every 
circle into 360 degrees. Whether the circle be large or small, 
it has the same number of degrees. The degrees of large cir- 
cles are longer than those of small ones. You will see that 

a2 



8 



ASTRONOMY. 



a part of this large circle is divided into single degrees ; and 
both circles are divided into halves and quarters. A quarter 
of a circle is 90 degrees : it is sometimes called a quadrant. 
A half of a circle is 180 degrees : it is often called a semicircle. 




DEFINITIONS. V) 

How many degrees are there in a circle ? How many degrees make 
a quadrant ? How many make a semicircle ? Are the degrees of all 
circles of the same length ? 

11. Degrees are sometimes divided into equal parts, called 
minutes ; and minutes into equal parts, called seconds. Sixty 
seconds make a minute, and sixty minutes a degree. De- 
grees are marked with a small cipher ; minutes with a small 
accent ; and seconds with a double accent. Thus, 10° 12' 
11" are ten degrees, twelve minutes, and eleven seconds. 

How many seconds make a minute ? How many minutes a degree ? 
How many degrees a circle ? Read these figures, 20° 14/ 17 /; . Read 
these, 140° 23' 39". 

12. A telescope is an instrument for looking at the sun, 
moon, planets, and other distant objects. It causes distant 
objects to appear nearer. There are several kinds of telescopes, 
hut they are all fitted with such glasses, as make distant 
objects appear larger and nearer, and thus enable us to see 
them better. 

What is the use of a telescope ? 



10 ASTRONOMY. 

CHAPTER I. 

THE SUN, ©. 

1. The Sim is a great globe : it is much larger than any- 
thing else that we know. When we look at it without a tel- 
escope, it does not appear to be more than one or two feet in 
diameter ; but the best telescopes make it appear very much 
larger. Astronomers have discovered several methods of as- 
certaining its size ; and they find its diameter to be more than 
860 thousand miles. The Sun is more than a million times 
larger than this earth. 

What is the shape of the Sun ? How great is its diameter ? What 
do you mean by the diameter of a globe ? How much larger is the 
Sun than the earth ? 

2. The Sun appears small, because it is so far from us. 
You know that all things appear smaller when distant, than 
when near you. A house can hardly be seen ten miles ; and 
a little fly that is quite near you, appears larger than an ox 
that is a mile off. The Sun is about 95 millions of miles 
from the earth. If a bird could fly towards it, at the rate of 
two miles every minute, it would require about ninety years 
to reach the Sun. 

Why does the Sun appear so small ? How far are we from the Sun ? 
How long would it take a pigeon, flying two miles every minute to 
reach the Sun ? 



THE SUN THE PLANETS. 11 

3. The Sun gives us light and heat, and you can easily 
understand that nothing in this world could live without it. 
It should remind us of the Lord, who is called the Sun of 
righteousness. His truth is the light o f our minds, and His 
love gives life to our souls. 

What do we receive from the Sun ? Of whom should the Sun remind 
us? 

4. The Sun appears to move round the earth every day, 
but this is not really the fact.. We shall explain this subject 
in another chapter. The Sun does, however, turn round on 
its own axis once in twenty five and a half days. 

Does the Sun revolve round the earth ? In what time does it revolve 
on its own axis ? 

Turn your ball round upon the stick that runs through it, 
and you will see how the Sun turns on its axis. 



CHAPTER II. 

THE PLANETS. 

1. There are eleven large globes, which revolve about the 
sun, and are called Planets. This earth on which we live is 
one of the Planets ; and w r e should not doubt that the others 
have inhabitants, who enjoy the manifold blessings of Him 
who is Lord over all. 



12 



ASTRONOMY. 



How many Planets are there? What is their shape? Do the 
Planets revolve round the sun, or does the sun revolve round the 
Planets ? 

2. The names of the Planets are Mercury, Venus, the 
Earth, Mars, Vesta, Juno, Pallas, Ceres, Jupiter, Saturn, and 
Uranus or Herschel. Mercury is the nearest to the sun, and 

-J- 




THE PLANETS. 



13 



you will see the comparative distances of all, except Saturn 
and Uranus, in this figure. These two are so much further 
than Jupiter, that there is not room here to represent their 
distances. Pallas and Ceres are so nearly at an equal dis- 
tance, that one circle is marked for both. 

What are the names of the Planets ? How many are nearer the 
sun than the earth is ? 



Circle. 



3. The line or path in 
which a Planet goes round 
the sun, is called its orbit. 
When a Planet is going 
round the sun, it does not 
keep at the same distance 
all the time ; but is some- 
times nearer the sun than 
at others. Hence its orbit is 
not a circle ; it is an ellipse. 
You will see the difference 
between a circle and an oval 
or ellipse by these figures. 



What is the orbit of a Planet ? What is the shape of the orbits of 
the Planets ? Is a Planet always equally distant from the sun ? 




14 ASTRONOMY. 

4. The time in which a Planet goes round the sun, is call- 
ed a year. You know that a year on this earth is 365^ 
days. It is 365 days when it is not leap-year, and 366 clays 
when it is leap-year; and, leap-year comes once in four years. 
Some of the Planets have much longer years, but Mercury 
and Venus have shorter. 

What is a year ? How long is a year on this earth ? How many 
days is the year in leap-year? Have any of the Planets longer years? 
Have any of them shorter years ? 

5. The time in which a Planet revolves once on its own 
axis, is a day. We begin our day at midnight, and divide it 
into 24 hours. Most of the Planets revolve in much less time 
than the earth does, and therefore have shorter days. 

What is a day ? At what time do we begin our day? Into how 
many hours is it divided ? Are the days on the other Planets just as 
long as ours ? 

6. We said that the Planets are not all of the same size. 
This picture will show the comparative size of most of them : 
the others are too small to be well compared in a picture. 
The marks, placed before the names of the Planets, are those 
which are often used instead of the names in Almanacs and 
books of Astronomy. 

Which Planet is the largest ? Which has a great ring round it? 
How many of the Planets are larger than the Earth ? 



THE PLANETS MERCURY. 



15 




7. Several of the Planets are frequently seen by us in clear 
evenings. They give a more steady, or less twinkling light, 
than the stars ; but most persons do not observe the differ- 
ence. 

Are any of the Planets ever seen by us ? How do they appear ? 



CHAPTER III. 
MERCURY, $. 

1. We shall now give a more particular account of each of 
the planets. Mercury is much nearer to the sun than either 



16 ASTRONOMY. 

of the others. Its mean distance is about 37 millions of miles. 
It is sometimes a little more, and sometimes a little less dis- 
tant; but this is its mean or average distance. 

Note. To find the mean or average of two numbers, add them to- 
gether and divide their sum by 2. To find the mean of three numbers, 
add them, and divide by 3. To find the mean of fifty numbers, add, 
and divide by 50. The same rule applies to all cases. Thus, find 
the mean of 4, 5, 6, 9. These make 24; and there are four distinct 
numbers. Divide 24 by 4, and the answer is 6. 

Which planet is nearest the sun ? How far is it ? Is it always just 
37 millions? What is the mean or average of 9, 8, 4, 11? If you 
walk a part of a day at 2 miles an hour, an equal part at 3 miles an hour, 
and an equal part at 4 miles an hour, how many miles an hour does it 
average ? If one boy can throw a stone 10 rods, and another boy can 
throw it 20 rods, what is the mean distance ? 

2. Mercury revolves on its axis from west to east once in 
24 hours, and revolves round the sun in about 88 days. 

How long is a day at Mercury ? How long is a year ? How many 
of our months are there in a year of Mercury ? How many seasons 
have we ? If Mercury has four seasons, how long is each ? 

3. Mercury never appears far from the sun. It is com- 
monly so near, that the brightness of the sun prevents our 
seeing it ; but it is sometimes visible a little after sunset. 
The apparent distance of a planet from the sun is called its 
elongation. Try now to understand this. Point your fin- 
ger towards the east. Now move it over slowly till it points 
to the west. It has moved just half 9. circle, and that is 18.0 



MERCURY. 17 

degrees. Move it now from the horizon to the zenith or the 
point directly overhead. That is a quarter of a circle or 90 
degrees. Half of the distance from the horizon to the zenith 
is 45 degrees. You will see this plainly by the figure on p. 8. 
Mercury never appears more than 28 degrees from the sun ; 
that is, its greatest elongation is 28°. 

Is Mercury often seen ? Why is it seldom visible ? What is the 
elongation of a planet ? How many degrees is it from east to west, or 
from any part of the horizon to the opposite part ? How far from the 
horizon to the zenith ? What is half that distance ? What is the 
greatest elongation of Mercury ? 

4. The sun appears to move round the earth once in 24 
hours. The whole distance that it appears to go, is a circle. 

How many degrees make a circle ? How many degrees does the 
sun appear to move in 24 hours ? How many in one hour ? How 
many in two hours ? How many hours does it take for the sun to ap- 
pear to move 90 degrees ? When the days from sunrise to sunset are 
twelve hours long, how many degrees does the sun appear to move in 
the day? 

Remember that the apparent motion of the sun and 
stars j is 15 degrees an hour. 

5. Mercury is a small planet ; it is about one fifteenth part 
as large as this earth. Its diameter is about '3000 miles. 

Is Mercury as large as this earth ? What is its diameter ? Recol- 
lect how much more the circumference of a globe or circle is, than its 
diameter ; and then find the circumference of Mercury. 



18 ASTRONOMY. 

6. Mercury is so much nearer the sun than this earth is, 
that the climate is probably warmer : but Ave do not know 
that it is warmer and lighter in proportion as it is nearer the 
sun. 

Is there probably more heat and light at Mercury, than we have ? 



CHAPTER IT. 

VENUS, ?. 

1. Venus is the most beautiful of all the planets that we 
can see. Its light is very white and pleasant. We see it 
very frequently for several hours in the evening, or early in 
the morning. Its greatest elongation, or apparent distance 
from the sun, is 47°. 

What is the appearance of Venus? Can we often see it? How 
many hours high does Venus ever appear after the sun sets ? How 
many hours does it sometimes rise before the sun ? The number of 
hours thai it sets after the sun, or ?ises before the sun, is found by seeing 
how many times 15 degrees there are in 47°. 

2. Venus is almost as large as the earth. Its mean dis- 
tance from the sun is 68 millions of miles : it revolves on its 
axis from west to east in a little less than 24 hours ; and re- 
volves round the sun in 7-J of our months. 

How large is Venus ? What is its mean distance from the sun ? 
How long is a day at Venus ? How long is a year ? 



VENUS. 



19 



3. When Venus is seen through a telescope it appears very 
differently from what it does to the naked eye. We do not 
see the whole of that half of it on which the sun shines, and 
therefore it does not appear round. You know how different- 
ly the moon appears at different times ; and Venus and Mer- 
cury have similar appearances when we look at them with a 
telescope. This picture will help you to understand what is 
here said. 

How does Venus appear when we look at it through a telescope ? 




4. You must remember that, neither the planets nor the 
moon give any light that is their own. The sun shines on 



20 ASTRONOMY. 

them, and they reflect some of the light to us. But the sun 
shines only on one side of a planet or moon at one time ; and 
the other side is dark. Sometimes we see but a small part of 
the side on which the sun shines, and then it does not appear 
round, nor give much light. 

Does Venus shine with her own light ? What gives it light ? Does 
the sun shine all around a planet or moon ? 

5. How delightful it is, to learn our own duty while we 
are studying these works of the Lord. The sun is the lord 
of this lower world. It gives light to all those globes tKat 
revolve about it ; and they send around to each other a part 
of what the sun gives them. So the Maker and Ruler of all 
worlds, imparts to us and to all his children the light of our 
minds, which is Truth ; and He requires that each one should 
impart to others from the light which he receives. 

Who gives light to all men ? What is that light ? What does He 
require of each one ? 

6. Mercury and Venus are sometimes called interior or in- 
ferior planets, because their orbits are within the earth's or- 
bit, or nearer to the sun. The orbits of the other planets are 
without the earth's orbit, or farther from the sun, and they 
are called exterior or superior planets. 

Why are Mercury and Venus called interior planets ? What are 
those called, that are farther from the sun than the earth is ? 



THE EARTH. 21 

CHAPTER V. 

THE EARTH, 0. 

1. The Earth on which we live does not appear like a globe 
when we look upon it ; but it is so large, that we can see on- 
ly a very small part of it If the smallest fly or bug were 
placed on an orange or an apple, it could see but a little dis- 
tance, and the parts around it would appear rough with hills 
and valleys, as the earth does to us. But we know that the 
Earth is a globe or sphere, because many men have sailed 
round it, which they could not do if it had a different shape. 
There are also other proofs that the Earth is a globe, which 
we shall attend to hereafter. 

What is the shape of the Earth ? How is this known ? 

2. The diameter of the Earth is about 8,000 miles. It 
turns round on its axis from west to east in about 24 hours, 
which make one day ; and revolves round the sun once in a 
year, or 365^. 

How many miles is the diameter of the Earth ? How many is the 
circumference ? Which way does it revolve on its axis ? How long 
is one revolution on its axis ? How long is a revolution round the sun ? 

3. Be careful to remember, that this Earth is a globe, or ball ; 
that it is a planet ; that it turns round from w-2st to east on 
its axis, and that the time in which it turns once round is 

B 



22 



ASTRONOMY. 



called a day : that it also goes round the sun, and that the 
time in which it goes once round the sun is called a year. 
What things must you carefully remember? 

4. If you hold your ball towards the sun or a candle, the 
light will shine on one half of it at a time. Turn it round 
from west to east, and each part will come to the light, and 
then go away from it every time that the ball turns round. 
In this way the sun shines on the Earth while the Earth turns 
round. If a fly were on the ball, the sun or candle would 
appear to the fly to move from east to west : so "while the 
Earth turns from west to east, the sun appears to move from 
east to west. This is like what you notice when sailing rap- 
idly in a boat or ship, or riding in a coach : the trees and 
houses, and fences which you pass, appear to move in the op- 
posite direction. 

On how great a part of the Earth does the sun shine at once ? Why 
does the sun appear to move from east to west ? 

5. Everything that is on this globe turns round with it ; 
and the air and clouds that are around us, also revolve with 
the Earth. It is because these things all move round quietly 
with us, that we do not notice their motion. So, when you 
sit in the cabin of a large boat or ship, and sail smoothly 
along, you cannot see that anything in the cabin moves. 
If you look out upon the land, the things which you there see, 



THE EARTH. 23 

appear to move backwards ; so. when you loo'c away from 
the Earth; and see the sun, mo^n. or stars, they appear to 
move backwards towards the west, because they do not go 
with the Earth. 

Do yon, and the trees, houses, and all things on the Earth, revolve 
with it once in a day ? Why do not these things appear to move ? 
Why do the sun, moon, and stars, appear to move from east to west? 

6. We revolve with the Earth once in a day. If we lived 
at the equator, we should go as far in a. day. as the whole 
circumference of the Earth : but we live nearly hallway be- 
tween the equator and the north pole. Now. measure round 
your ball at the equator : then measure round it about half 
way from the equator to the pole. You find the distance 
much less here, than at the equator. Make a little dot at 
the equator, and another where you last measured round the 
ball. Now. revolve it slowly ; and you can see that the last 
dot does not go so far in revolving once, as the other does. It 
revolves in the same time, but goes slower. Those people, 
therefore, who live at the equator, revolve 24,000 miles in a 
day : but others revolve slower, and a less distance in a day, 
in proportion to their distance from the equator. 

Do you move as fast with the Earth, as the people at the equator ? 
How far do they move in a day ? Why do you not go as far ? 

7. As the people at the equator are carried about 24,000 
miles in a day, they must be carried a twenty fourth part of 
b2 



24 ASTRONOMY. 

that distance in an hour, and that is 1000 miles. The peo- 
ple of Philadelphia, and other places in latitude 40°, are car- 
ried 800 miles in an hour. The people of Boston, and others 
in latitude about 42J° are carried 770 miles in an hour. The 
people of St. Petersburgh, and others in latitude 60°, are car- 
ried about 500 miles in an hour. 

How far are people at the equator carried in a day by the Earth's re- 
volution on its axi3 ? How far in an hour ? How far are those carried 
who live in latitude 40° ? Those in latitude 42J° 1 Those in 60° ? 

8. You will now understand about the Earth's motion on 
its axis ; and we will proceed for a while to talk of other 
things. 



CHAPTER VI. 



THE MOON, D, 



1. The eleven planets that we have mentioned, are called 
'primary planets. Some of them have a small kind of plan- 
ets that revolve about them, and go with them round the sun. 
These are called Moons, secondary planets, or satellites. 
Mercury and Venus have no Moons ; our Earth has one ; 
some of the planets have several Moons. 

Have Mercury and Venus any Moons ? How many has the Earth ? 
Has any planet more ? 



THE MOON. 



25 



2. The beautiful Moon, which shines on the earth so 
sweetly in the night, is 240 thousand miles from us. It re- 
volves round the earth, as a little ball round a large one, in 
29 J days ; and it revolves on its axis in the same time. 

How far is the Moon from the earth ? In what time does the Moon 
go round the earth ? How long is a day at the Moon? 

3. The diameter of the Moon is about 2000 miles. To 
the people of the Moon the earth appears as the Moon does 
to us, except that it probably appears much larger. 

How large* is the Mcon ? How does the earth appear to the luna- 
rians, or inhabitants of the Moon ? 

4. When we look at the Moon through a telescope, it has 
a very rugged appearance. Those parts which are brightest 
are supposed to be high lands and mountains ; .and the dark- 
er parts to be valleys. The cut on the next page will give 
you some idea of the appearance of the Moon when seen 
through a telescope. 

What are the brightest parts of the Moon supposed to be ? What 
are the darker parts ? 

5. There is but little air about the Moon, and probably lit- 
tle water upon it. *We could not live there ; but it is doubt- 
less a very good world for such people as live there- 
Is the Moon supplied with air and water so well that we could live 

on it ? 



26 



ASTRONOMY. 




6. You must remember that the Moon does not shine with 
its own light ; it receives light from the sun, and reflects it to 
us. The earth also receives light from the sun, and reflects 
it to the Moon and the other planets, 



MARS. 27 

Does the Moon shine with its own light ? Whence does it receive 
light ? We shall explain several other important things concerning the 
Moon in another part of this book. 



CHAPTER VII. 

MARS, &. 

1. We now begin to speak of the planets that are further 
from the sun than this earth is. Mars is 144 millions of 
miles distant, and revolves round the sun in a little less than 
2 of our years. It revolves on its axis in about 25 hours. 

Is the earth, or Mars, farthest from the sun ? How far is Mars 
from the sun ? How long is a year at Mars ? If a boy were born at 
Mars at the same time that you were born, how many years of Mars 
has he lived ? How many years of Mercury ? How much longer is 
a day at Mars, than our clay ? 

2. Mars is about 4,309 miles in diameter. It is not, there- 
fore, more than one third as large as our globe. To the peo- 
ple who live on Mars, this earth probably appears larger than 
Mars does to us. But Mars is one of the brightest planets, 
and appears of a fiery red color. 

How large is Mars ? How does it appear to us ? 

3. When we look at this planet through a telescope, we 
can see many singular spots and belts upon it, as in this cut. 



28 



ASTRONOMY, 



We know not what is the cause of these appearances. Pos- 
sibly they may be clouds. Mars has no moon. 

What singular appearances are mentioned? Do you know the 
cause of them? Has Mars any moon? 




VESTA, JUNO, PALLAS, AND CERES. 29 

CHAPTER VIII. 

VESTA g, JUNO 5, PALLAS $, AND CERES ?. 

1. We shall treat of all these planets in one chapter, be- 
cause we know little of them. It is but a short time since 
they were discovered. Ceres was discovered in 1801, by Piaz- 
za of Palermo in the island of Sicily ; Pallas, by Dr. Gibers 
of Bremen, in 1802 ; Juno, by Mr. Harding near Bremen, in 
1804 ; and Vesta by Dr. Gibers, in 1807. All these planets 
are very small, and we do not know that they have any 
moons. 

When, and by whom, was Ceres discovered? — Pallas? — Juno? — ■ 
Vesta ? Are they large, or small ? -Have they any moons ? 

2. Vesta is about 223 millions of miles from the sun. 
Its year is equal to 3 years and 8 months on this globe. We 
do not know how long its day is, nor what its diameter is. 

How far is Vesta from the sun ? How long is its year? Do you 
know the length of its day ? 

3. Juno has a very elliptical orbit. Its mean distance from 
the sun is 253 millions of miles ; but it is sometimes much 
greater, and sometimes much less. Its year is equal to 4 years 
and 4 months on this earth ; and its day is supposed to be 
27 of our hours. 

What is the mean distance of Juno from the sun ? In what time 



30 ASTRONOMY. 

does it revolve round the sun ? In what time does it revolve on its 
axis ? 

4. Pallas is sometimes almost twice as far as at other times 
from the sun. Its mean distance is about 263 millions of 
miles. Its year is equal to about 4 years and 7 months on 
this earth. We know not the size of Pallas, nor the length 
of its day? 

How great is the distance of Pallas from the sun ? Is it always 
equally distant? How long is the year of Pallas ? 

5. Ceres is about as far from the sun as Pallas, and its 
year is about the same length. The length of its day, and 
its size, are unknown. 

How far is Ceres from the sun ? How lono- is its vear ? 



CHAPTER IX. 

JUPITER, n. 

1. We come now to a planet of prodigious size, which we 
shall be better able to describe than we were the last four. 
Jupiter's diameter is 89,170 miles. It is 1400 times the size 
of this earth ; and is the largest planet that we know. 

What is the diameter of Jupiter? — the circumference? — its size 
compared with the earth ? 



JUPITER. 31 

2. Jupiter is 490 millions of miles from the sun ; thus, it 
is about five times as far as we are. Its revolution round the 
sun requires about 12 of our years ; but it revolves on its axis 
in abeut 10 hours. 

How far is Jupiter from the sun ? How long is its year ? — its day ? 
How many of Jupiter's years are there in 48 of ours? How many in 
96'? How many of Jupiter's days are equal to 10 of ours? 

3. Jupiter gives us a beautiful light, and it is the brightest 
of all the planets except Venus. If it were as near as Venus, 
it would appear like a great moon. When Jupiter is seen 
through a telescope, it appears to be crossed with belts, that 
change their position and figure at different times. Many 
lingular spots are also seen on its face. The next cut repre- 
sents some of these appearances. 

What is said of the brightness of Jupiter ? How would it appear, if 
it were as near as Venus ? How does it appear through a telescope ? 

4. Now we have something to say, that is very curious. 
Jupiter has four moons, or satellites, which revolve round it as 
our moon revolves round the earth. Some of them are small- 
er than our moon, and some are much larger. They are at 
very different distances from Jupiter, and revolve round it in 
different times. One of them goes round in about 2 of our 
days, and none of them requires more than 17 days. You 
recollect that our moon requires 29£ days. 



32 



ASTRONOMY. 




How many moons has Jupiter ? What is said of their size ? — of the 
times of their revolutions ? 

5. The inhabitants of any one place on Jupiter can seldom 
or never see all the moons at one time, but they frequently 
see two or three. As the planet revolves in 10 hours, the 
days and the nights are very short ; and neither the sun nor 
any of the moons can ever be long absent. If we could see 
all these spots, belts, and moons, as the people of Jupiter (Jo, 
how strange they would appear. 

Are all the Moons of Jupiter often visible at one time ? Are they 
Ion of absent? 



SAT U UN. 33 

6. It is not probable, that the people of Jupiter can see 
either Mercury, Venus, the Earth, or Mars. Ail these planets 
appear nearer the sun to l hem, than Mercury does to us ; and 
the brightness of the sun's light would prevent their being- 
seen. Those planets which are beyond Mars, can be seen 
from Jupiter, and perhaps others are visible, of which we know 
nothing. 

What planets are probably invisible at Jupiter ? Why can they not 
be seen ? What is the elongation of a planet ? What planets are vis- 
ible at Jupiter? 



CHAPTER X. 
SATURN, h. 

1. Here is another wonderful planet. Saturn is larger 
than any other except Jupiter. Its diameter is 79,000 miles, 
and it is 1000 times larger than this earth. 

What is the diameter of Saturn ? Its circumference ? How much 
larger is it than this earth ? 

2. Saturn is 900 millions of miles from the sun, and re- 
volves round it in 30 of our years. It revolves on its axis in 
about 10 hours. 

How far is Saturn from the sun ? How much farther than the earth ? 
How long is its year ? — its day ? 



34 ASTRONOMY. 



3. When seen through a telescope, Saturn appears to be 
surrounded by two rings. One ring seems to be within the 
other, and there is a considerable space between them. You 
can form some idea of them from this cut. 

What is said of Saturn's rino-s ? 



4, This singular planet has seven moons. They revolve 

in different times, varying from 1 day to 80 days. These 

moons, and the bright rings, doubtless render the nights at 
Saturn very light and pleasant. 

How many moons has Saturn? In what times do they revolve? 
W hat mak e Saturn's nights pleasant ? 



URANUS OR HERSCHEL. 35 

CHAPTER XL 

URANUS or HERSCHEL, #. 

1. The people of the continent of Europe commonly call this 
planet Uranus ; but in England and America it has been 
more common to call it Herschel. It was discovered to be a 
planet by Dr. Herschel of England, in the year 1781. Many 
others had previously seen it. but they supposed it to be a fixed 
star. 

When, and by whom, was this planet discovered? What had others 
supposed it to be ? 

,2. Uranus is the most distant from the sun of all the plan- 
ets that we can see. Its distance is 1800 millions : which is 
twice as far as Saturn, and nineteen times as far as the earth. 

How far is Uranus from the sun ? How much farther than Saturn ? 
— than the earth ? 

3. One revolution of this remote planet round the sun re- 
quires 84 of our years. If its inhabitants do not live longer 
than those of our earth, few of them live to be a year old. 
The length of their day is unknown. 

How long is a year at Uranus ? 

4. The diameter of Uranus is 35,000. It is, therefore, the 
third planet in size, and is 90 times the size of this earth. 
Six moons revolve round Uranus, but they are so far from us, 
that we can know little of them. 



36 ASTRONOMY. 

How large is Uranus ? How many planets are larger ? How many 
moons has Herschel ? 

5. The immense distance of Uranus from the sun would 
lead us to suppose that it roust be very dark and cold. But 
the people may receive more heat and light from the sun, 
than we are aware of, and they may have better means than 
we know of for producing light and heat. Their eyes may 
be fitted to see where we could not ; and their bodies may not 
be so easily affected by the cold. Some animals have eyes 
that see best where there is little light ; and some cannot live 
except in cold climates. So also, there are some vegetables 
that will not grow where the climate is very warm ; and oth- 
ers cannot bear the cold. He who is the Creator and Pre- 
server of all things, mercifully adapts them all to the stations to 
which He appoints them, and to the uses which He designs 
them to perform. 

Is it certain that the climate of Uranus is very cold, and that the 
people have little light? Are animals and vegetables adapted to va- 
rious degrees of heat and light? 

6. We have now described all the planets that we are ac- 
quainted with. There may be others so small or so distant 
that we cannot see them with our telescopes. Five of those 
which we now know, have been discovered since the year 
17S0 ; and if further improvements should be made in the 
telescope, others may perhaps be seen. 



COMETS. 37 

Is it certain that no more planets revolve round our sun ? How 
many have been discovered since 1780 ? Can you tell which they 
are ? 



CHAPTER XXL 

COMETS. 

1. There is a class of bodies revolving about the sun, 
which appear very different from the planets. They some- 
times come very near the sun, and are seen by us for a con- 
siderable time ; and then they go far away, so that they can- 
not be seen with the best telescopes for many years. They 
appear somewhat like a planet or star, except that they have 
a bright train or tail extending from them, and spreading out 
to a great distance. These singular bodies are called Comets. 
The cut on the next page represents the Comet that ap- 
peared in 1811. Its tail was much longer than it here appears. 

Do Comets ever come near the sun? Are they always visible ? 
How do they appear ? 

2. Although Comets generally appear small like stars, some 
have been seen which looked as large as the moon. The 
tails of some Comets are short, and give but little light ; but 
others extend as far as from the horizon to the zenith, or 90 
degrees, and give as much light as a small moon. This dif- 

c 



ASTRONOMY. 



ference in their appearance sometimes depends on their 
distance. 




COMETS. 39 

How large have any Comets appeared ? How far do any of their 
tails extend ? 

3. We do not know enough about Comets, to describe 
theni so well as we do the planets. Only a few, and those 
not very large, have appeared since astronomers have had 
good telescopes, and have understood well how to calculate 
the size, distance, and revolutions of such bodies. About 500 
are known to have been seen within the last 1800 years ; but 
the time of revolving round the sun has been determined for 
only two of them. We cannot tell when the large ones will 
be seen again. 

Why can we not well describe the Comets ? How many have been 
seen within 1800 years ? Are the periods of their revolutions known ? 

4. The Comet that is best known is called the Encke 
Comet, because its revolution was first accurately calculated 
by Professor Encke of Germany. This is a very small 
Comet, and revolves round the sun in about 1200 days. It 
goes nearer the sun than Mercury, and farther from it than 
Ceres. It never appears large to us. 

What Comet is best known ? How long is its revolution round the 
sun ? How near the sun does it go ? How far from it ? Does it ever 
appear large ? 

5. It is not four hundred years since Comets were regarded 
with extreme terror, because they were supposed to be the 
forerunners of dreadful calamities * but we now regard them 

c2 



40 



ASTRONOMY. 



without any fear, and class them among the good things 
which the Lord has made. They may be inhabited like the 
planets ; but even if they are not, we cannot doubt that they 
are useful ; for wftat the Lord has made, he made to do 
good. 

How were Comets formerly regarded ? How are they now regard- 
ed ? For what did the Lord make all things ? 



CHAPTER XIII. 
METEORS. 

1. Meteors are bright bodies, that are often seen darting 
through the atmosphere. They do not appear to revolve in 
orbits, like planets and comets, but to fly about in various di- 
rections. Some of them are called fa Ring stars, or shooting 
stars, and are often seen moving along rapidly, and leaving 
a long train or tail behind them. 

What are Meteors ? Do they appear to revolve in regular orbits ? 
What are some of them often called ? 

2. Meteors commonly appear no larger than a star ; but 
some have been seen that appeared as large as the sun, and 
brighter than the moon. Most of them move very rapidly, 
but others slowly. 

What is said of the size of Meteors ? — of their motion ? 






METEORS. 



41 



3. We are generally incapable of giving any probable esti- 
mate of the distance of these bodies. In many cases the same 
Meteor has appeared in the same manner to persons who 
were many hundred miles apart. This shows that they are 
commonly at a much greater distance than they appear to be. 

What is said of their distance ? 

4. In some cases, however, they have been noticed so near, 
that they were heard to make a loud buzzing noise, as they 
rushed through the air. Some have also been heard to burst 
with a tremendous noise ; and stones have been seen to fall 
from them to the ground. In the year 1807, one was seen 
passing over the town of Weston, in Connecticut. It appeared 
nearly as large as the sun, and very bright. It burst with a 
great explosion, and large stones fell to the ground. All the 
stones that were found, would, perhaps, weigh 300 pounds. 
They were of a different kind from any that belong to this 
country ; and when they fell, they were hot. Similar explo- 
sions have been noticed in other places. 

Have Meteors ever been known to be near the persons who saw 
them ? What sometimes happens with them ? What is said of the 
Meteor seen in Connecticut in 1807? 

5. It is not, however, supposed, that all Meteors are com- 
posed of stones ; but we do not know much about them. 
We are entirely ignorant how such stories happen to be far 
above the earth, and moving about in every direction. Nei- 



42 



ASTRONOMY. 



ther do we know why they are hot, nor why they are so 

luminous. 

Are all Meteors supposed to be composed of stones? Is it known 
how they are produced ? 

6. In the year 1779 a most wonderful appearance of Mete- 
ors was seen in the eastern sky. Thousands; and probably 
millions, of Meteors were seen within the space of four hours; 
and some of them seemed twice as large as the sun. They 
were noticed in South America, Labrador, Greenland, and 
Germany. Their height must have been immense, to be 
seen, at the same time, at places so far distant from each other : 
and their size must have been very great, or they could not 
have appeared so large when at so great a distance. 

What is said of the remarkable appearance of Meteors, witnessed 
in 1779? 



CHAPTER XIV. 

THE FIXED STARS. 

1. We have now spoken of the Sun, the Planets, Moons, 
Comets, and Meteors. We call the Sun the centre of this 
system ; and all the other globes that we have described re- 
volve round the Sun, and depend upon it for light and heat. 
When we thus speak of the Solar System, we mean the 
Sun, and all the globes that revolve round It. 



THE FIXED STARS. 13 

What is meant by the Solar System? What bodies have we de- 
scribed, that belong to this System ? 

2. But there are other globes in the firmament, that do not 
belong to this System. Most of those bright, twinkling 
bodies, which you see in a clear evening, are called Fixed 
Stars. We call them fixed, because they have no real mo- 
tion that we can discover. These Stars are, doubtless, sun- 
to other systems ; that is, they are like our sun, and have 
planets revolving round them. 

Why do we call these Stars jixed'J What are they supposed to be ? 

3. When you look at the Stars, in a clear evening, their 
number seems immense, but you really see but few, com- 
pared with what you suppose you see/ You look at them 
confusedly, instead of separately and distinctly ; and that cau- 
ses the delusion. You can seldom see more than 1,000 in 
the finest evenings, unless you look through a telescope. 

How many Stars can you see at one time without a telescope ? 
Why do they appear to be so very numerous ? 

4. W ben we look through a telescope we can see manv 
Fixed Stars that are otherwise invisible ; but all of them are 
at so great a distance, that a telescope does not have any ef- 
fect to bring them near, and make them appear larger, as it 
does the planets. If they were not more than 200 thousand 
times farther from the sun than this earth is, we could esti- 
mate their distance ; but no one of the Fixed Stars is within 
that immense distance. 



44 ASTRONOMY. 

Can we see more Stars with a telescope, than we really see without 
one ? Does a telescope, magnify them, as it does the planets ? 
How far from the sun might they be, and, yet, their distance be esti- 
mated ? 

5. We often see a broad belt extending from northeast to 
southwest, which appears somewhat like a white cloud, and 
seems to be filled with an infinite number of small Stars. 
This belt is called the Milky- Way or Galaxy. When we , 
look at it through a telescope, we find that it does actually con- 
sist of very great numbers of Stars, which are divided into 
clusters. 

What is the white belt called, extending from northeast to south- 
west ? Of what is it composed ? 

6. The Stars were divided into clusters or constellations ', 
by persons who lived several thousands of years ago : and 
names were given to the constellations, and also to the princi- 
pal Stars in each cluster. One of these clusters is called Ori- 
on : the yard L, is nearly in the middle of it. Another is 
called Pleiades, or the Seven Stars. Both of those are men- 
tioned in the book of Job, which is supposed to be the oldest 
in the world. The ancients reckoned 50 constellations. 
Modern astronomers have added many others. 

Who divided the Stars into clusters, and named them ? In what 
ancient book are two of them mentioned ? How many clusters did 
the ancients reckon ? 

7. If you have a celestial globe, you mav see about 100 



THE FIXED STARS. 45 

constellations named, and also the names of the largest Stars. 
The Stars are reckoned in six classes, according to their size. 
The largest class are said to be of the Jirst magnitude ; those 
considerably smaller are of the second magnitude. Thus 
they are numbered to the sixth class, which are the smallest 
that can be seen without a telescope. 

How many constellations are now reckoned ? Into how many 
magnitudes are the Stars divided? 

8. There are many other things respecting the Fixed Stars, 
which you will find it very interesting and useful to learn 
when you are a little older. But you are old enough now, to 
consider how great, and manifold, and full of wisdom and 
goodness, are the works of the Lord. Behold the Fixed 
Stars, which are so many Suns, with Planets revolving round 
them ; and these Planets : with their Moons, are peopled with 
innumerable beings, who daily receive the rich blessings of 
the Divine Providence. When the Lord had made these 
things, He saw that they w x ere very good. They are called 
good, because He made them to do good. You are made 
for the same purpose, and you should be diligent and faithful 
to perform it. 

For what purpose did the Lord make all things ? 



46 ASTRONOMY. 

CHAPTER XV. 
THE FOUR SEASONS. 

1. We have given a general account of the Sun, Planets. 
Moons, Comets, Meteors, and Fixed Stars ; and we shall now 
explain more fully several important things respecting the 
planet on which we live, and the moon that revolves round it. 

Of what have we given a general account ? Of what are we now to 
give a more full explanation ? 

2. There are four Seasons, viz. Spring, Summer, Autumn, 
and Winter. Spring is partly cold and partly warm ; Sum- 
mer is quite warm ; Autumn is generally mild ; and Winter 
is very cold. These different Seasons are caused by the dif- 
ferent manner in which the sun shines on us, at these differ- 
ent periods of the year. 

How many seasons are there ? What is said of each ? What 
causes the different Seasons ? 

3. You will recollect that the earth revolves round the sun 
once in a year, or in 365^ days. During a part of the time 
that the earth is thus going round, the equator is turned di- 
rectly towards the sun, as you see by the cut oppasite. 

When the sun shines thus on the earth, those persons who 
live at the equator have it directly overhead every day at noon. 
We live considerably north of the equator, and therefore th^ 



THE FOUR SEASONS. 47 

sun is never vertical, or directly overhead ; and . it is so with 
those w T ho live far south of the equator. The days when the 
sun is exactly vertical at the equator, are the 2Uth of March, 
and the 22d of September. 

At what times of the year is the sun directly overhead at the 
equator ? 





4. From the 20th of March to the 21st of June, the north 
part of the earth is turned gradually more and more towards 
the sun ; so that the sun is vertical one degree north of the 
equator, and then two degrees, and so on, till it is 23° 28' 
north of the equator. That happens on the 21st of June, 

This degree of latitude on the earth is called the Tropic of 
Cancer. It passes over the island of Cuba, across Mexico. 
the southern cape of California, the island of Formosa, China, 
and many other countries, as you may see by a map. This 



48 



ASTRONOMY. 



cut will show, you how the earth is so turned, that the sun 
shines more directly on the northern parts of it. 

During what period is the northern part of the earth inclining 
more and more towards the sun ? How far north of the equator is 
the sun ever vertical ? When is it so far north ? What is that line 
round the earth called, on which the sun is vertical on the 21st of 
June ? 





5. From the 2 1st of June, the earth is gradually turned so 
that the declination of the sun diminishes every day till Sep- 
tember 22d. By the declination of the sun we mean its ap- 
parent distance from the equator at noon. When it is vertical 
at the equator, it has no declination ; when it is any number 
of degrees north or south, we say its declination is so many 
degrees. 

When does the earth get turned back, so that the sun is vertical 
again at the equator? What appears by the 4th paragraph to be the 



THE POUR SEASONS. 



49 



greatest northern declination of the sun ? In other words — How far 
north of the equator is it ever vertical ? Remember what the declina- 
tion of the sun means. 

6. From the 22d of September until the 22d of Decem- 
ber, the southern part of the earth is gradually inclined to- 
wards the sun. Then the sun has southern declination, or 
is vertical to places south of the equator. Its declination in- 
creases gradually till it is 23° 28'. Then it is at the Tropic 
of Capricorn. This cut will show the southern part of the 
globe inclined towards the sun. 

During what part of the year does the sun's southern declination 
increase? When is it greatest? How great is it at that time ? 





7. From December 22d to March 20th, the earth gradually 
comes back to the position that makes the sun shine vertically 
at the equator. Then it has completed a year, and has had 
the sun vertical once, as far north as the Tropic of Cancer, 



50 ASTRONOMY. 

twice at every place between the Tropic of Cancer and the 
Tropic of Capricorn, and once at the Tropic of Capricorn. 

When does the earth turn back, so that the sun is vertical at the 
equator ? How many times in a year is the sun vertical at the Tro- 
pics ? — at all places between the Tropics ? 



CHAPTER XVI. 

THE FOUR SEASONS CONTINUED. 

1. You can now see that we have our warmest weather 
when the northern part of the globe is inclined towards the 
sun, and our coldest weather when the southern part of the 
globe is inclined towards the sun. 

When have we the warmest weather ? When the coldest ? 

2. When we have Spring, those who live in south latitude 
have Autumn ; when we have Summer, they have Winter ; 
when we have Autumn, they have Spring: when we have 
Winter, they have Summer. Thus, their Seasons are oppo- 
site to ours. 

What Season have the people of New Holland, the southern part 
of Africa, and the southern half of South America, when we have 
Spring? — When we have Summer? — When we have Autumn?— 
When we have Winter ? 

3. By the following cut you will plainly see why the sun 



THE FOUR. SEASONS. 



51 



gives us more heat in Summer than in Winter. Look care- 
fully at it, and observe how much more oblique or slanting 
the Winter rays are, than the Summer rays ; and that more 
of the latter fall on any given space, than of the former. 
Thus you will understand why we have less heat in propor- 
tion as the sun's rays fall obliquely. If you do not fully com- 
prehend this, ask some one to assist you. 
Whv have we less heat in Winter than in Summer ? 




4. The earth is not nearer to the sun in Summer than in 
Winter ; on the contrary, it is a little nearer in Winter. If 
that has any effect, it tends to make the Summer in south lat- 
itude a little warmer than the Summer in north latitude ; for 
the earth is nearest the sun, when it is Summer in south 
latitude. 



52 ASTRONOMY. 

When is the earth nearest the sun ? 

5. iVfter the earth on this part of the globe has become quite 
cold by a Winter, it requires considerable time to get warm : 
and after it has become quite warm, it requires considerable 
time to grow cold. For this reason, the weather does not 
become warm in Spring till the sun has been this side of the 
equator some weeks ; and when it has become warm, it con- 
tinues to grow warmer, even after the sun r begins to return 
from the Tropic* of Cancer towards the equator. Thus our 
warmest month is July, or .sometimes August, although the 
sun is farthest north on the 21st of June. The sun is at the 
equator in March and September ; but March is much colder 
than September, because it comes directly after a cold Winter, 
whereas September follows Summer. 

Why is not our March as warm as our September ? When is our 
warmest weather? When has the sun most northern declination? 
When has it most southern declination ? Is the weather commonly 
coldest in our climate at that time ? 



CHAPTER XVII. 

THE FIVE ZONES. 



1. From what we said in the last two chapters, you will 
find it very easy to understand the meaning of the Zones. 




THE FIVE ZONES. 53 

All that part of the earth that ever has the sun vertical, is called 
the Torrid Zone. You will see that it extends an equal dis- 
tance each side of the equator. This 
part of the globe is always warm. There 
is no winter ; and snow and ice are never 
seen, except on the tops of very high 
mountains. The sun is vertical over 
every part of this Zone twice in a 
year. 

Where is the Torrid Zone ? What line passes through the middle 
of it ? What is said of its climate ? 

2. The Northern Temperate Zone is next northward of 
the Torrid Zone. It extends from the Tropic of Cancer to 
the Arctic Circle, in latitude 66° 32'. When the sun is north 
of the equator, this Zone has warm weather ; but when the 
sun has southern declination, the weather in this Zone is 
cold. The climate of the Northern Temperate Zone is much 
colder in the northern parts of it, than in the southern. 

How far does the Northern Temperate Zone extend? What is its 
climate ? 

3. The Southern Temperate Zone extends from the Torrid 
Zone to the Antarctic circle, in latitude 66° 32 south. The 
climate of this Zone is like that of the Northern Temperate 
Zone ; but it has opposite seasons, as we showed in the last 
chapter. 



54 ASTRONOMY. 

Where is the Southern Temperate Zone ? What is said of its cli- 
mate? — of its seasons ? 

4. The Frigid Zones extend from the Polar circles to the 
Poles. When the sun's declination is one degree north, it 
shines continually without setting, for a space of one degree 
from the North Pole. As the sun's northern declination in- 
creases from March 20th to June 21st, the space where it re- 
volves without setting becomes broader. Its breadth from the 
Pole is just equal to the sun's declination ; so that on the 21st 
of June the whole of the Northern Frigid Zone has constant 
day. If you look at the figure on p. 48, you will see that 
the sun shines round the North Pole for a considerable dis- 
tance, when that part of the earth is turned towards the sun. 

Where are the Frigid Zones ? When the sun's declination is 5 C 
north, how much of this Zone has constant day ? How much when the 
sun is at the Tropic of Cancer ? 

5. As the sun's declination diminishes, this space also di- 
minishes which has constant day ; and on the 22d of Sep- 
tember the sun ceases to have any northern declination. 
Observe that when it is constant day in the Northern Frigid 
Zone, it is constant night in the Southern Frigid Zone ; and 
just so much of one of these Zones has constant night, as 
there is of the other that has constant day. So, as the sun 
has southern declination from September 22d to March 20th ? 



DAY AND NIGHT. 55 

the Southern Frigid Zone has then its summer and its long 
days. 

When there is constant day for 10° about the North Pole, what is 
there for 10° about the South Pole ? When the sun's declination is 
20° south, where is there constant day ? — where is there constant 
night ? 

6. Although the days are very long in summer in the Fri- 
gid Zones, and during a part of the time the sun is constantly 
visible, yet its rays fall so obliquely that they do not make 
the weather warm for many days at a time. The snow and 
ice remain in many places during the whole year. Scarcely 
anything grows near the Poles for the support of man or of 
beast. The winters are intensely cold, and are rendered ex- 
tremely dismal by the darkness. 

What is the climate of the Frigid Zones ? Why is it not very warm 
in summer? 



CHAPTER XVIII. 

DAY AND NIGHT. 

1. From what has already been said, you probably under- 
stand the cause of day and night ; but it may be useful to at- 
tend more to the subject, and repeat some things that we 
have said. 

d2 



56 ASTRONOMY. 

2. The earth revolves on its axis from west to east in 24 
hours, or one day. As it makes a complete revolution or cir- 
cuit in 24 hours, it moves a twentyfourth part of it in 1 hour ; 
and a twentyfourth part of 360°, is 15°. Thus the earth 
turns 15° in an hour. 

In what time does the earth revolve on its axis ? How many de- 
grees does it turn in an hour ? 

3. While the earth is turning round, the sun shines on but 
one half of it. That half has day, and the other half has 
night. Hold your ball in this manner towards the sun or a 





lamp, and then turn it slowly from west to east, and you will 
explain to yourself the cause of day and night. 

On how great a part of the earth does the sun shine at any moment? 

4. Now, stick a little piece of paper on your ball nearly half 
way between the equator and the North Pole, and call it the 
U?iited States. Turn the ball so that the United States 
w T ill be on the top of it, oi directly under the zenith. When 
it is noon, the sun shines on the country where w T e live, just 
as it will on the piece of paper upon your ball. 



DAY AND NIGHT. 57 

Where is the zenith ? How are you to hold the ball with the United 
States on it, so as to show how the sun shines on us at noon'? 

Observe that you must do this at noon, or else turn the ball so as to 
make the sun shine on it as it would at noon. 

5. Now turn the ball from west to east about one quarter 
of a revolution. A little fly or bug. standing on that paper, 
would now see the sun towards the west, just setting. Turn 
it further, and the sun could not be seen. When the paper 
comes to the nadir, or the point opposite the zenith, it is situa- 
ted as we are at midnight. Turn the ball further till the fly 
could see the sun, and you will observe that it would see it 
rise in the east. 

If a fly stood on the paper while you revolve the ball, where would 
it see the sun set? Where would it see the sun rise ? 

If the scholar find this explanation too difficult, he must he careful to 
obtain assistance from some one who ivill make it perfectly plain. 

6. In the chapter on the Seasons } r ou saw that the sun 
shines more on the northern hemisphere when its declination 
is north, and more on the southern hemisphere when its de- 
clination is south, and equally on both hemispheres when it 
has no declination. The sun has no declination when it 
shines vertically at the equator, that is, on the 20th of March 
and the 22d of September. 

What is meant by the declination of the sun ? When does the sun 
shine most on the northern hemisphere ?— on the southern hemisphere ? 
When does it shine equally on both? 



58 ASTRONOMY. 

7. The 20th of March is called the venial equinox, and 
the 22d of September is called the autumnal equinox. They 
are called equinoxes, because the nights and days are then 
equal in every part of the globe ; that is, the nights are 12 
hours long, and the days are 12 hours long, at the equator, 
and in north latitude, and in south latitude. 

What are the equinoxes^ How long are the days at those times?— 
the nights ? Are they the same in all places ? 



CHAPTER XIX. 
DAY AND NIGHT CONTINUED. 

1. During all the time that the sun's declination is north 
— namely, from March 20th to September 22d — the days are 
longer than the nights in the northern hemisphere. They 
grow longer every day till June 21st, and then diminish, as 
the sun's declination does, till September 22c! . 

What part of the year is the sun's declination north ? What effect 
has that upon the days in the northern hemisphere ? During what 
time are they gradually becoming more than twelve hours long? 

2. At the equator the days and nights are of about equal 
length at all seasons of the year ; but a little north of the 
equator the days are a little longer than the nights when the 
sun's declination is north ; and the farther north we go, the 
greater is the length of the days during that period. 



DAY AND NIGHT. 



59 



Where are the days and nights always about equally long ? Does 
the length of the days increase as you go farther towards the pole ? 

3. The following table will show the length of the longest 
day in several degrees of latitude. 





f 

s 




n 


1 ;K 

1 ^ 


De 2 . 




Hours 
12 


Mm, 
00 


Des. Mm. 
66 32 


Days. Hours- 

1 


12 


12 


42 


68 


42 1 


20 


13 


12 


70 


64 14 


30 


13 


56 


72 


82 7 


32 


14 


6 


74 


96 17 


34 


14 


16 


75 


104 1 


36 


14 


28 


78 


122 17 


38 


14 


38 


80 


134 5 


40 


14 


52 


82 


145 7 


42 


15 


4 


84 


156 3 


44 


15 


18 


85 


161 5 


50 


16 


10 


87 


171 22 


55 


17 


8 


89 


181 22 


60 


18 


30 


90 


187 6i 



What is the length of the longest day in latitude 20°?— in latitude 
40° ?— in latitude 72° ? What is the length of the longest day at the 
city of Mexico? — at Philadelphia? — at Boston? — at St. Petersburg ? 
— at Spitzbergen? — at Cape Horn ? — at Potosi? 

4. The two hemispheres are directly opposite in respect to 
the length of days and nights, as they are in respect to sea- 
sons. When those who live in north latitude have longer 



60 ASTRONOMY. 

days than nights, those who live in south latitude have short- 
er days than nights. Our longest day and their shortest day 
is June 21st. Our shortest day and their longest day is De- 
cember 22d. Their nights are always as long as our days, 
and our nights as long as their days. Observe, however, that 
in all calculations of this kind you must have respect to the 
latitude of places, as we have in the following questions. 

When the day is J 3 hours long in latitude 40° north, where is the 
night 13 hours long ? When the night is 16 hours long in latitude 
60° north, where is the day 16 hours long ? When there are shorter 
days than nights in south latitude, are they the same in north latitude ? 
What is the longest day in north latitude ? — in south latitude ? What 
is the length of December 22d in latitude 60° south ? See the Table, 

5. When you know the length of a day, subtract it from 
24, and it will leave the length of the night. Subtract the 
length of the night from 24, and it will leave the length of 
the day. 

When our days are 16 hours long, how long are our nights ? When 
our nights are 13 hours 20 minutes, how long are our days ? How 
long is the shortest night, where the longest day is 22 hours ? 

6. When you know the time of sun-rise at any place, dou- 
ble it, and you will have the length of the night. Double the 
time of sun-set, is equal to the length of the day. 

When the sun rises at 5 o'clock, how long is the night ? How long 
then is the day ? When the sun sets at half past 7, how long is the 
day ? How long then is the night ? 



DAY AND NIGHT. 61 

7. At all places nearer the poles than the polar circles are. 
the sun revolves without setting during a part of the year, and 
without rising during an equal part. The longest day. there- 
fore, in all these places, is more than 24 hours ; and the long- 
est night is of the same length. At the poles, the sun shines 
constantly for six months, and is absent for six months. See 
the Table. 

Where are the longest days more than 24 hours ? How long is the 
longest night where the longest day is two months ? How many days 
are there in a year at the north pole ? How many nights ? How 
many nights in a year at the south pole ? How many days are there 
in a year, where the sun shines continually for sixty of our days, and 
does not rise for sixty days ? The time when it is constantly seen, and 
the time when it is constantly absent, properly make one day. Sixty and 
sixty make 1*20. Subtract this from 365, and add the 1 day to the re- 
mainder, and it will give the answer. 

8. There is about a week when the sun is very near the 
Tropic of Cancer, and another week when it is very near the 
Tropic of Capricorn. During those times it changes its de- 
clination very little ; and, therefore, it rises and sets at nearly 
the same time for several days. Thus, we have several days 
that are almost as Ions: as the longest, and several almost as 
short as the shortest. These times, about the 21st of June 
and 22d of December, are called the solstices. The former is 
the summer solstice ; the latter the winter solstice. 

When is the summer solstice ? — the winter solstice ? 



62 ASTRONOMY. 

9. For some time before the sun rises, and after it sets, it 
shines upon the air and clouds so as to give considerable light. 
This time in the morning and evening is called tioilight. 

What time is called twilight ? 

10. Near the equator there is but a very short time of twi- 
light. Almost as soon as the sun sets, dark night commences. 
But as we go toward the poles, the time of twilight increases ; 
and in some parts of the frigid zones where the sun is absent 
for several months, there are many days of twilight. 

Where is there little twilight? Where is there a great deal ? 



CHAPTER XX. 

DIFFERENT PHASES OF THE MOON. 

1. By the different phases of the Moon, we mean its dif- 
ferent appearances. You know that it sometimes appears 
horned^ in this manner, <j. Sometimes it is like half a globe; 
and sometimes it is like a whole globe, thus, @. Its face does 
not look black like these marks ; but these marks show its 
different shapes. 

What is meant by the phases of the Moon? 

2. In order to understand the cause of these appearances, 
you must recollect again, that the Moon revolves round the 



DIFFERENT PHASES OF THE MOON. 



63 



earth once in 29J days : that the Moon is a dark body like 
this earth, and only gives light when the sun shines upon it: 
that the sun shines upon only one half of the Moon at one 
time, and therefore one half of it is dark : and that the sun 
shines only a part of the time on that side of the Moon which 
is towards the earth. 

In what time does the Moon revolve round the earth ? Is the Moon 
a luminous body, like the sun ? Whence does it receive light ? How 
great a part of the Moon is enlightened by the sun at one time ? Does 
the sun always shine on that part of the Moon which is towards us ? 





3. Now examine this figure carefully. >S. is the Sun ; E. 
is the Earth ; A, B, C, D; E, represent the Moon in differ- 
ent parts of its orbit. When the Moon is between, or nearly 
between, the earth and the sun, its dark side is directly to- 
wards the earth. This will appear plainly from the Gut : for 



64 ASTRONOMY. 

when the Moon is at A. only the dark side of it is towards E ; 
and it would appear to one who stood at E. as it does at a. 
This is the state of the Moon, when we say it changes , and 
becomes new moon. 

What state of the Moon is represented by its appearance at A? 

4. One or two days after the Moon changes, it is so far 
east of the sun, that we can see a small part of the side upon 
which the sun shines. For three or four days it continues to 
be horned. See how the sun shines on it at B ; and observe 
that its shape appears to us as at b. 

How long after the change does the Moon appear horned ? 

5. When it has gone one quarter of the way round the 
earth, as at C, we say it quarters. We then see half of the 
side on which the sun shines, and it appears like half a globe. 
It is a little more than 7 days from the change to the first 
quarter. 

How does the Moon appear, when it has gone one quarter of a revo- 
lution ? How many days is the first quarter after the change ? 

6. When the Moon has passed its first quarter, it appears 
more than half round, because we see more than half of the 
side on which the sun shines. It is then called gibbous, and 
appears as you see at d. 

When the Moon is more than half round, what do we call its shape ? 

7. When it is opposite the sun, as at E, we see all that 
side of it that is enlightened ; as at a. It is then full moon. 



DIFFERENT PHASES OF THE MOON. 65 

When is it full moon ? 

8. By looking at the remainder of the figures, you will see 
that the Moon wanes or decreases from full moon till new 
moon, as it waxes or increases, from neio moon till full moon ; 
and that it has the same phases or appearances during the 
two quarters before new moon, as during the two quarters 
after neio moon. 

During which part of the Moon's revolution is it said to wax ? Dur- 
ing which is it said to wane ? What phases has the Moon between 
full moon and new moon ? 

9. It is frequently convenient to know the age of the Moon, 
that is, the number of days since it changed. If it is not 
more than 7 days old, it shines only in the early part of the 
evening ; from the time that it is 7 days old till it is 14 or 15 
days old, it not only shines early in the evening, but also quite 
late ; when it has changed, it rises later every evening, till it 
ceases to be an evening Moon ; and during its last quarter it 
shines only for a little while before day-light. 

During what time does the Moon shine when it is not more than 7 
days old? — from 7 days to 14 or 15 days old?— after it changes? — 
during its last quarter ? 



66 ASTRONOMY. 

CHAPTER XXL 

ECLIPSES OF THE SUN. 

1. We have mentioned that the moon revolves round the 
earth once in 29-J days. It sometimes comes directly between 
the Sun and the earth, so as to prevent the Sun from shining 
on some part of the earth. This is the cause of an Eclipse 
of the Sun. This cut will show you how the moon's shadow 
falls on the earth; and prevents our seeing the Sun. 



What causes an eclipse of the sun? 

2. When the moon hides the whole face of the Sun, there 
is a total eclipse : when it hides only a part of the Sun, it is 
a partial eclipse. Sometimes it hides all except a small rim 
or ring, and that makes an annular eclipse. Total eclipses 
and annular eclipses are very uncommon. 

Define the three kinds of eclipses. Which are uncommon ? 

3. The shadow of the moon can cover only a small part of 
the earth. For this reason we see but few of the eclipses of 



ECLIPSES OF THE SUN. 67 

the Sun, and but few are seen by the people of any particular 
part of the globe. 

Is there ever an eclipse of the Sun at all places on the earth at the 
same time ? Do we see all the eclipses that happen ? 

4. The following Table will tell you what great eclipses of 
the Sun will be seen in America during the remainder of this 
century. 

1834, Nov. 30. It will be total in South Carolina. 

1836, May 15. It will be annular in the West Indies. 

1838, Sept. 18. It will be annular in the western part of Connecticut, 
in New York, New Jersey, Pennsylvania, Maryland, Del- 
aware, Virginia, and North Carolina. 

1854, May 26. It will be annular at Boston, and a part of New Hamp- 
shire and Maine. 

1865, Oct. 19. It will be annular in North Carolina and South Caro- 
lina. 

1869, Aug*. 7. It will be total in North Carolina and Virginia. 

1875, Sept. 29. It will be like the eclipse of 1854. 

1900, May 28. It will be total in Virginia. 

When will the next total eclipse of the Sun occur in any part of the 
United States ? When will the next annular eclipse occur in Boston ? 
— in New York ? 

5. The last total eclipse of the Sun in any part of the 
United States, was in 1825 ; but that was total only in a 
small part of Florida. The last that was seen by us, was in 
June, 1806. There will not be another that will be total in 
any part of New England during this century. 



68 ASTRONOMY. 

When was the last total eclipse of the Sun in any part of the United 
States ? When was the last that was seen by the people of several of 
the States ? Will there soon be another in New England ? 



CHAPTER XXII. 
ECLIPSES OF THE MOON. 

1. The Moon sometimes passes through the shadow of the 
earth, and that causes an Eclipse of the Moon. Hold up 
your ball to the sun, and it will cast a shadow for a consider- 
able distance. The earth casts a great shadow for a very- 
great distance. When the Moon is in this shadow, the sun 
does not shine on it. 

What causes an eclipse of the Moon? 




2. Sometimes only a part of the Moon passes through the 
earth's shadow, and then there is only a partial eclipse ; but 
when the whole Moon passes through the shadow, there is a 
total eclipse. There cannot be an annular eclipse of the 
Moon. 



ECLIPSES OF THE MOON. 



69 



How is a partial eclipse of the Moon caused ? — a total eclipse ? 

3. Eclipses of the Moon are also called lunar eclipses. 
Although no eclipse of the sun is visible on a large part of the 
earth, yet every eclipse of the Moon is visible to all who can 
see the Moon. We therefore see more lunar eclipses than 
solar eclipses. 

What other name is given to eclipses of the Moon ? Are they visi- 
ble on more of the earth than solar eclipses ? Do we see more solar 
eclipses, or lunar eclipses ? 

4. An eclipse of the Moon can only happen at the time of 
full Moon. An eclipse of the sun can only happen at the 
time of new Moon. But, there is not an eclipse of the sun at 
every new Moon, nor an eclipse of the Moon at every full Moon. 

When do lunar eclipses happen ? Is there an eclipse of the Moon 
' at every full Moon ? When do solar eclipses happen ? Is there an 
eclipse of the sun at every new Moon ? 

5. The causes of eclipses of the sun and Moon have been 
known only a few centuries. Especially when a total eclipse 
of the sun occurred, the ancients w T ere filled with wonder and 
fear. But we are now as well able to account for eclipses, as 
for any more common event ; and we can calculate the exact 
times when they occurred in past ages, and will occur during 
thousands of years to come. 

Have the causes of eclipses been long known ? Can they now be 
accurately calculated ? 
E 



70 ASTRONOMY. 

CHAPTER XXIII. 

LEAP YEAR. 

1. We have already stated that the earth revolves round 
the sun in 365^ days ; and, as we call one revolution a year, 
we are obliged to reckon 365 days to each year for three suc- 
cessive years, and 366 days to every fourth year. The years 
that have 366 days, are called leap years. 

What are leap years ? 

2. The day that is added, in order to make leap years have 
366 days, is always added to February. For three successive 
years February has but 28 days ; and every fourth year it 
has 29 days. 

To what month is the day added to make leap year have 366 days ? 
How many days has February in leap year ? 

3. To ascertain when it is leap year, divide the year by 4, 
and if there is no remainder, that year is leap year. If there 
is a remainder, that remainder will show how many years 
have passed since leap year. Thus : take the year 1831, and 
divide it by 4, and the remainder will be 3. It is, therefore, 
3 years since leap year, and consequently the next year will 
be leap year. Divide 1832 by 4, and see whether we have 
judged right. You will find that there is no remainder. 

How do you ascertain when it is leap year? If there is a remainder 



LEAP YEAR ATTRACTION. 71 

after dividing by 4, what does it show ? How long after leap year, 
was 1827 ? Was 1816 leap year ? How many days were there in 
February in 1820 ? How many in 1813 ? 

4. This mode of measuring years, or the periods of the 
earth's revolutions, is very nearly correct, but is not perfectly 
so. Adding one day in every four years, is a little too much, 
and therefore the day is omitted once in a century. Thus, 
the year 1800 was not reckoned leap year, although it was 
the fourth after leap year, and could be divided by 4 without 
any remainder. So the year 1900 will not be reckoned as 
leap year. By thus omitting once in a century to add the one 
day to every fourth year, w T e measure the time w T ith such ex- 
actness, that several thousand years will not make an error of 
one day in our manner of measuring the earth's revolutions. 

How often is it necessary to omit adding one day when the year can 
be divided by 4 without any remainder? 



CHAPTER XXIV. 
ATTRACTION. 

1. There are several kinds of attraction ; and 3^011 will 
understand them w 7 hen w r e mention some examples, A load- 
stone attracts iron, and this is called magnetic attraction, or 
the attraction of magnetism, Take a load-stone, or a piece 



72 ASTRONOMY. 

of iron that has been rubbed with load-stone, and hold it near 
any very small piece of iron or steel ; and you will see that 
it attracts or draws it. 

What will a load-stone attract? What kind of attraction is this ? 

2. The little particles that compose a piece of wood, stone, 
apple, lead, iron, and most other things, attract each other. 
It is because the particles attract each other, that these things 
keep their proper shape, instead of crumbling into dust. This 
attraction, which makes the particles of bodies cohere, or stick 
together, is called the attraction of cohesion. 

What prevents your ball from crumbling into little particles of dust? 

3. If you keep one corner of a handkerchief dipped in 
water, the whole handkerchief will soon become wet. So, if 
you dip one end of a piece of sugar in your tea, the sugar will 
attract the tea, and make it rise so as to wet the whole. This 
is called capillary attraction. 

If I dip one part of a sponge in water, the whole will soon be wet ; 
what kind of attraction causes this ? 

4. The attraction w T hich causes bodies, that are above the 
earth, to fall towards it, is called the attraction of gravitation. 
When your feet are tripped, you fall towards the earth, and 
not towards the clouds. Throw a stone into the air, and it 
will not go far ; the earth will attract it, and pull it down. 

Why do bodies fall towards the earth ? What kind of attraction is 
it, that prevents your jumping to the moon? 



ATTRACTION. 73 

5. The attraction of gravitation also makes all kinds of 
bodies have weight. Their weight is not always in proportion 
to their size ; for a pound of sponge is much larger than a 
pound of lead. The lead is more solid or dense, and there- 
fore has more matter in the same bulk. All bodies are at- 
tracted by the earth in proportion to their quantities of matter, 
and their weight is in the same proportion. 

What makes bodies have weight ? Why is a bushel of stones 
heavier than a bushel of corn ? Which is most dense, corn, feathers, 
or iron ? In what proportion are bodies attracted by the earth ? In 
what proportion are they heavy ? 

6. Observe that the density of bodies is not the same as 
their hardness. Lead is more dense than stone, or iron, but 
it is not so hard. We know that lead is the most dense, 
because it is the heaviest; and we know in the same way that 
it has the most matter in it. Platina is the most dense sub- 
stance, and therefore the heaviest, that we are acquainted 
with. Gold is next in density and weight. But there are 
many substances much harder than platina or gold. The 
attraction of cohesion makes bodies hard, but the attraction 
of gravitation makes them heavy. 

Is the density the same as the hardness of bodies ? What is the 
most dense and heaviest substance that we know ? What is next in 
density and weight 1> What makes bodies hard? What makes them 
heavy ? 



74 ASTRONOMY. 

7. As all bodies are attracted to the earth in proportion to 
their quantities of matter, they are in no danger of falling or 
going away from the earth. It makes no difference whether 
they are on one side of the earth, or on another ; for the earth 
attracts nearly equally on all parts of its surface. This is the 
reason why people may live on all parts of the earth, notwith- 
standing it is round, and is turning round very rapidly every 
moment. Besides this rapid motion on its axis, the earth goes 
68 thousand miles every hour in its orbit round the sun. 
Still, we are in no danger of falling off, and being left behind 
to fly in the air. 

What keeps all bodies from falling off from the earth ? Are they 
attracted on all sides of the earth? How fast does the earth move 
round the sun ? 



CHAPTER XXV. 
ATTRACTION CONTINUED. 

1. We have said that the earth attracts all bodies in pro- 
portion to their quantities of matter ; and it is also true, that 
other bodies attract each other. My desk attracts my ink- 
stand, knife, scissors, books, spectacles, and all other things 
that are near it : and all these things attract each other. A 
large mountain attracts with considerable power, and causes 






ATTRACTION, 75 

the clouds to gather round it. and leave water to form the 
springs. 

Do nearly all bodies attract each other ? Why do the clouds gather 
about the mountains ? 

2. All bodies have the power of attraction in proportion to 
their quantities of matter: and the earth has so much more 
matter than any of the bodies that are on its surface, that its 
attraction is incomparably greater. For this reason we seldom 
notice the attraction of small bodies for each other : all are so 
much attracted by the earth, that they seem not to be drawn 
by each other. 

In what proportion have all bodies the power of attraction? Why 
do we not feel the attraction of a tree, a mountain, or a house ? When 
you drop an apple or a stone, why is it not drawn away to some tree, 
mountain, or rock, that is near ? 

3. The earth is supposed to attract all bodies more, the 
nearer they are to its centre. A stone, or bird, or anything 
else that is far above the earth . is less attracted than it would 
be nearer the earth. The moon is a great way off. but still it 
is somewhat attracted by the earth, and also attracts the earth. 
If the earth and moon were nearer each other, the attraction 
between them would be greater. So all other bodies, when 
near each other, attract more than when distant. A moun- 
tain will not draw a cloud to it, that is many miles distant. 

Does the earth attract bodies when they are near it, more than when 



76 ASTRONOMY. 

they are distant? Do the moon and the earth attract each other? 
Would they attract less, or more, if they were nearer ? 

4. The sun has a great deal more matter in it, than any 
planet, or anything else that we know. It has, therefore, 
immense power of attracting the planets and all things in this 
solar system. It does not attract the things on this earth so 
much as the earth does, because it is so far distant ; but it at- 
tracts the earth and all the planets enough to keep them re- 
volving in their proper orbits. 

What object has more matter in it, than any other that you know? 
What does the sun attract? W T hen you throw up a stone, does the 
earth, or the sun, attract it most? What keeps the earth and the 
other planets revolving* in their proper orbits ? 

5. If you fasten a stone, or any other body that will weigh 
two or three pounds, to one end of a string, and swing it round 
you rapidly with the other end, you will find that it pulls you 
quite hard. The faster you make it revolve, the more it will 
draw you. You thus perceive that it has a tendency to fly 
away in a straight line, instead of revolving in a circle. If 
you let go the string when the body is revolving rapidly, it 
will thus fly away for some distance. 

When you twirl a stone round you with a string, or a sling, does it 
incline to come towards you, or to fly away ? Has it a tendency to 
move in a straight line, or in a circle ? 

6. When you are twirling the body round you, it draws 
you with considerable force ; and that force is called the cen- 



ATTRACTION. 77 

trifiigal force. You have to exert considerable force to pre- 
vent its flying away from its proper circle or orbit ; and that 
force is called the centripetal force. 

What is that f-nrce called, which keeps a body that is revolving, from 
going to the centre of its orbit, or draws it away from the centre ? 
What force is tint, which is required to prevent a body that is revolv- 
ing, from flying away in a straight line ? 

7. Now, consider that the sun and earth attract each 
other, and therefore have a tendency to come together. This 
is the centripetal force. By revolving rapidly round the sun, 
the earth has a tendency to fly away out of its orbit. This is 
the centrifugal force. These two forces are exactly equal to 
each other : and therefore the earth is not drawn to the sun, 
nor does it fly away from it in a straight line ; but it revolves 
round the sun continually, in a regular orbit, as you make a 
stone revolve round you, when you twirl it with a string. 

What force is the attraction between the sun and the earth called ? 
What opposite force is just equal to this ? What is the effect of these 
two forces ? 

8. In the same manner all the planets are attracted by the 
sun, and are prevented by their centrifugal force from being 
drawn to it ; and in this way they are all kept in their proper 
orbits. So, likewise, the earth and moon attract each other ; 
and the centrifugal force which the moon acquires by revol- 
ving round the earth, prevents their coming together, and 

F 



78 ASTRONOMY. 

keeps them at their proper distance. The moons of the other 
planets are regulated in the same manner. 

Are all the planets kept within their proper orbits in the same man- 
ner as the earth is kept in its orbit? What prevents the moon from 
flying away ? What prevents its coming to the earth ? Why do not 
Jupiter's moons go away to the sun, or some other planet ? Why do 
they not fall upon Jupiter, and kill the cattle and the inhabitants ? 



CHAPTER XXVI. 
TIDES. 

1. We have shown that the earth attracts the moon, and 
keeps it in its orbit. The moon also attracts the earth, and 
has a great effect on the water and the air. The moon's at- 
traction raises up the air and the waters of the ocean on that 
side of the globe that is turned towards the moon, and makes 
them much higher than they are in other places. This is the 
cause of Tides. 

What effect has the moon's attraction on the waters of the ocean ? 

2. The sun's attraction has also some effect on the water ; 
and when the sun and moon are both on the same side of the 
earth, they produce the greatest tides, which are called spring 
tides. When the sun and moon are on opposite sides, so 



THE TIDES TIME. 79 

that the attraction of one counteracts that of the other, they 
produce the least tides, which are called neap tides. 
How are spring tides caused ? How are neap tides caused ? 

3. There are two tides in a day ; for there is one tide on 
the side of the earth next to the moon, and one on the oppo- 
site side. The water is about 6 hours in rising or floioing^ 
and 6 hours in falling or ebbing. 

How many tides are there in a day ? During how many hours is it 
flood tide ? During how many is it ebb tide ? 

4. The tides occur later from day to day, as the moon rises 
later ; but it is not far from half a clay from high water to 
high water again, or from low water to low water again. 

Do the tides constantly occur at the same hour of the day ? 

5. The tides are not equally high in all places. Some 
parts of the ocean rise 30 or 40 feet ; and other parts do not 
rise more than 2 feet. 

Are the tides equal in all places ? How high are they ever known ? 



CHAPTER XXVII. 

TIME. 

1. When the sun comes to the meridian of any place, we 
call it noon at that place ; but it does not come to the meri- 



80 ASTRONOMY. 

dian of every place at the same time, and therefore it is not 
noon at every place at the same time. Those places that 
have the same longitude as the place where you are, have 12 
o'clock and other hours when you have. Those that are 
one degree east of you, have 12 o'clock and other hours 4 
minutes earlier than you have ; and those that are one de- 
gree west of you, have all times 4 minutes later than you 
have. Allow 4 minutes for each degree, or one hour for 15 
degrees, and you can easily count the difference of time be- 
tween any two places. You must reckon the nearest way 
from one place to another, so as not to make the difference 
more than 12 hours. 

When it is noon in Boston how much after noon is it at a place 10° 
east of Boston? When it is 4 o'clock at Albany, how much does it 
want of 4 at Buffalo ? — at Cincinnati ? When it is midnight at New 
Orleans, what time in the morning is it at London ? How much ear- 
lier does the sun rise at Philadelphia than at St. Louis ? — than at Li- 
ma ? — than at Mexico ? How much later does the sun rise at Natches, 
than at Norfolk ? — than at Paris in France ? — than at Rome in Italy ? 
Find the difference of longitude between the above places, by a gazetteer, 
or globe. 



FINIS, 




003 630 037 1 



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